Enhancing precipitations by applying soluble complex fluorine-containing reagents



ENHANCmG PRECIPITATIONS BY APPLYING SOLUBLE COMPLEX FLUORINE-CONTAINING RELALGJZIN'IS Glenn W. Sta'hl, Richland, Washi, assignor to theUnited States of- America as represented by the United States Atomic Energy Commission No Drawing. Application June 4, 1945 Serial No. 597,593 16 Claims. (c1. 23-145 This invention relates to a procedure for the processing of materials containing the element of atomic number 94, known as plutonium, for separating the plutonium from extraneous matter such as substances of the kind present in neutron irradiated uranium as exemplified by uranium and especially fission products, and the like radioactive contaminants. More particularly, this invention concerns a separatory and concentration procedure involving the use of supplemental additions, such as fiuosilicic acid, whereby improved decontamination and Pu recovery may be obtained.

As described herein, the isotope of element 94 having a mass of 239 is referred to as 94 and is also called plutonium, symbol Pu. In addition the isotope of element 93 having a mass of 239 is referred to as 93 Reference herein to any of the elements is to be understood as denoting the element generically, whether in its free state or in the form of a compound, unless indicated otherwise by the context.

Elements 93 and 94 may be obtained from uranium by various processes which do not form a part of the present invention including irradiation of uranium with neutrons from any suitable neutron source, but preferably the neutrons used are obtained from a chain reaction of neutrons with uranium.

Naturally occurring uranium contains a major portion of U a minor portion of U and small amounts of other substances such as UX and UX When a mass of such uranium is subjected to neutron irradiation, particularly with neutrons of resonance or thermal energies, U by capture of a neutron becomes U which has a half life of about 23 minutes an d by beta decay becomes 93 The 93 has a half life of about 2.3 days and by beta decay becomes 94 Thus, neutron irradiated uranium contains both 93 and 94 but by storing such irradiated uranium for suitable period of time, the 93 is converted almost entirely to 94 In addition to the above-mentioned reaction, the reaction of neutrons with fissionable nuclei such as the nucleus of U results in the production of a large number of radioactive fission products. As it is undesirable to produce a large concentration of these fission products which must, in view of their high radioactivity, be separated from the 94 and further as the weight of radioactive fission products present in neutron irradiated uranium is proportional to the amounts of 93 and 94 formed therein, it is preferable to discontinue the irradiation of the uranium by neutrons when the combined amount of 93 and 94 is equal toap proximately 0.02 percent by weight of the uranium mass. At this concentration of these substances, the concentration of fission elements whichmust be removed is ap' proximately the same percentage.

A number of processes have already been proposed'fo'r type of process.

2,86,408 Patented May 1 2 T959 accomplishing the separation and concentration of'Pu. Certain of these processes are generically known as the bismuth phosphate type process and the wet fluoridef These processes are the invention of others and the processes are described in co-pending applications, as for example applicationSer. No.-5-l9,714, now Patent No. 2,785,951, to be referredto hereinafter, which gives detailsrelative to such processes;

It is sufiicient to indicate at this point that by means of such processes, of which there are a number,v applied in one or several cycles dependent uponthe concentration of contaminants and similar considerations the contamination may be substantially reduced and the plutonium recovered. That is, as described above, the desired plutonium to be recovered is in the presence of substantial quantities of fission products evidenced by beta and gamma activities, and the plutonium must be isolated from at least a portion ofthe activity. In other words, the activity preferably is eliminated either completely or at least to a certain tolerance level so that the Pu may be handled or further used without danger from radioactivity due to contaminants. The bismuth phosphate method of by-product and product precipitation is generally illustrative of processes which may be applied to separate and recover plutonium. f

Thus while existing processes, including the bismuth phosphate type of process, are quiteefiicient-an'd successful, it may be necessary torepeat the decontamination cycles a number of times in order to-obtain a Pu in which the activity has been eliminated or reduced to the tolerable amount. As set forth in application Serial No. 519,714, filed January 26; 1944, of Thompson and Seaborg, now Patent No. 2,785,951, it has been" discovered that plutonium has more than one oxidation state, including a lower oxidation state or states referred to here in as Pu in which the element ischaracterized by forming insoluble phosphates and other insoluble compounds and a higher oxidation state or states referred 'to as Pu in which the element forms soluble phosphates and other soluble compounds.

That is, by having the metal as Pu a product precipitation or extraction may be accomplished in which a carrier precipitate such as, for example, bismuth phosphate brings down the Pu" leaving behind in solution a substantial portion of fission products and othersources of contamination. However, some of the activity in the form of contaminants such as barium, columbium, zirconium, andlanthanum activities may be carried down with the Pu and may be quite difficult to separate from Pu. Further the amount of these latter fission products could be reduced by a decontamination cycle consisting of a by-product precipitation and a product precipitation using, for example, BiPO as a carrier.

For carrying out such a cycle, a carrier precipitate containing Pu" and activity from the first extraction, or from a-previous product precipitation, after suitable dissolution, may be oxidized so that Pu is obtained. The Pu remains in solution and a by-product carrier precipitate, such as a bismuth phosphate by-product precipitate, under the oxidizing conditions can carry down fission products leaving the Pu in solution. However, in this step certain by-product precipitate fines may not separate out or otherwise some contamination may remain so that the solution remaining which contains the Pu may still be contaminated with some fission products although in much smaller amounts. It should be kept in mind that since" the Pu is in an environment of radioactivity which may give many millions of counts a aesaaos procedure termed out; Sea ve ngin ribed n the c prob sej are hilly; desc I I bore; SenNos- I7 on of Thorgnnsongand Se Po solutions the I precipitation step above described. I I I I I I 3 the zirconium activity can he precipitated as. m'r 1 coniurn phosphate by adding zirconium phosphate to the solution: of oxidized: Pat and fission prod nets. l iGtherexamples and; a more. complete Sex isclosedin th {A Product extractiofi :Metat soiutio step (Z) Extraction :of as from soiuti Decontamination; cycle: f a 1 I (11') {By-product precipitation stepis)? with: scavengera r 1 December, 15 he issen e ate rel ases and the like I pita .I

' y ptoti n? from? .I I ikniii s I iagjentjsilj h asiis dum if; i; 1,; ;'v 1 1 I oxalic acid or the like in excess for a neridd'of To the solutionofPM about one hour at a temperature from 50 C. to of bismuth ion to provide a concentration of his- 75 C. whereby any of the Pu metal, some of Inuth ion equivalent to 10 grams of Bi, ion in which may have been oxidized to the Pu state four liters of solution. Phosphoric acid is also in the solution step, is reduced to the Pu state, added to make the solution between 0.30 M and hvdrazine is eliminated or other action takes place. 1.20 M therein. A precipitate, comprising BiPO, The uranyl nitrate concentration of the solution which carries Pu comes down and is separated is adjusted to 20% based on uran vl nitrate hexafrom the solution. This completes the product hydrate and under existing practice H 80 is added. precipitation step and the decontamination cycle To the solution is now added a source of bismuth which consists of the by-product precipitation step ion to provide a concentration of bismuth ion and product precipitation step.

equivalent to 10 grams of Bi' ion in four liters REPEAT-ED CYCLES thereof. Phosphoric acid is also added to make the solution between .3-.8 M the ein, d a pre- If it is desired to remove additional fission products Cipitate comprising BiPO which carries th P 0 from the Pu obtained from the foregoing procedure, the omes down and is separated fr th l ti by decontamination cycle may be repeated therewith, befiltration or centrifugation. This illustrates the ginning with the Solution of the BiPO4 Product precipitate extraction 1' product precipitation from a unan l in nitric acid, followed by oxidation and the other denitrate solution. contamination cycle steps above described. This de- (B) Decontamination cycle: contamination cycle may be repeated as often as desired. (1) By-product precipitation stepdepending upon the desired degree of elimination of The BiPO precipitate from the Extraction Step fission Productswhi h carries the F n) is di l i 10 N NO The exact manner of obtaining the bismuth phosphate The acidity of the solution is reduced to 6 N HNO Product and y'p precipitate-S other Carrie! P by dilution and the solution made 0,01 M i cipitates is not a limitation on the present invention.

3- ar us other oxidizing agents, such a Various amounts and sources of bismuth and phosphate potassium dichromate, permanganate, and the like, ions may be used. Details respecting these aspects are y al e used. Another oxidant such as potasdescribed in other co-pending applications and form no sium dichromate, may be added in o e ti integral part of the present invention. Consequently, in with the primary oxidant, sodium bismuthate, to certain of the description which follows, reference will peroxid eems:

, are mentioned for hold the Pu in the oxidized state after all bismerely be made to a product or by-product carrier, or mutilate s been reduced or decomposed. On similar terms used, it being apparent that such carrier may heating the solution at 50 C. for 1 hour, the be formed in any suitable manner, one of which methods plutonium is oxidized to the Pu state. The solu- ,has been illustrated above. tion is then diluted to 1 N acidity by addition of mentioned, in all existing processes, including the 'BiP'O process above described, separatism o'f #Pu -from fission products is not clean cut. For example, -'in 't;he extraction of Pu from auranyl'nitr'at'e solution, the BiPO carries practically all ofthe product but also some of'the fission activity. Likewise, in the by-product precipitation, with or without scavengers, the by-product precipitate does not carry all of the fission activity'but leaves some fission activity in solution with the oxidized'Pu.

In the separation of the by-product precipitate, Whether by centrifugation, filtration, or other means, some "of the finely divided by-pro'duct precipitate containing fission activity passes the centrifuge, filter or other means, and

thus is "carried over into the product precipitation step.

The presence oft'hese residues of fission activity'fr'oni "the by-product precipitation during product precipitation has been found 'todiminish materially the decontamination of the Pu obtained "in the product precipitation step.

I have found that the aforementioned separ'atdry and recovery processes which are referred to herein'as existing, standard or conventional processes, exemplified by thebisr nuth phosphate process, may haveincluded therein certain supplemental agents and operations for improvin such processes.

The present invention is supplemental to the existing processes and is designed to obtain more clean cut separations, a more favorable decontamination factor in fewer steps or cycles, or a higher decontamination factor, namely, more complete decontamination than formerly was possible by the particular process, in the same number of steps, and to effect a higher recovery of 'Pu.

The meaning of the terms, contaminants, bismuth phosphate type of process, product and by-productprecipitate, decontamination, and similar terms are apparent to some extent from the preceding description and will be further apparent as the description proceeds.

The invention has for one object, to provide improvements in methods for the separation and recovery of plutonium.

Another object is to provide a method of separating plutonium by a procedure wherein certain additional materials and steps supplemental to or in place oftho's'e heretofore used are employed.

Another object is to provide an improved procedure -for eliminating, eradicating, or lessening gamma contamination.

Another object is to provide improved procedures in forming by-product and product carrier precipitates, and in improving other phases of recovery processes.

Still another object is to provide a procedure for improving decontamination.

Still a further object is to improve decontaminationand product recovery by steps and addition materials which lend themselves to combination with steps already known or practiced.

Another object is to provide a type of process which may employ materials used in'existing processes, but with more effective decontamination, and which maybe carried out in existing equipment without change, or with a'ininimum of equipment change.

Still another object is to improve'existingprocedures by reducing the number of cycles required for decontamination or by obtaining higher decontamination with the same number of cycles.

Another object is to provide a process susceptible of treating sources of Pu containing concentrationsthereof and activities higher than heretofore encountered.

Other objects will appear hereinafter. v

I have confirmed that Pu in admixture with various extraneous materials may be separated andconcentrated by the use of the series of steps involving the formation of certain carrier precipitates, as above described. The formation of these precipitates may be similar to existing practices in many features as respects some of the reagents, temperatures and similar aspects.

I have found that processes of the aforementioned'types f6 involving the use' of precipitates for carrying contaminationa'way from Pu andcar rying Pu away from contamination maybe improved at many points, from the extraction step to-the productprecipitation step, and even to the step of cleaning out-the equipment, by use of fiuosilicic acid type reagent as set forth in detail herein.

For example by the carrying out of extraction under the conditions of'th'e'present invention not only are the advantages of the prior processes retained but additional advantages, such as the precipitation of less barium, zirconium and columbium in this step are obtained.

The present invention comprises the use of flue-reagents in processes'of recovery of transuranic elements, such as Pu, for the purposes of effecting a better separation of fission product's and of increasing the yield of the transuranic elements.

More specifically thepresent-invention comprises the use'of iiuo-rea'gents 'for the purpose of complexing zirconium, columbium and uranium so that they can be removed from solutions or materials in which they are contained along with other material from which it is'desired -to separatethe'rh, and'which, if the solution or material is radioactive, results in the removal of fission products.

The solutions containing Pu which may be treated by my invention may be the same type of solutions as heretofore treated, or may be solutions in which the concentrations of components are much higher.

As'apparentfrom the foregoing, one common type of solution containing Pu subject to separation and recovery procedures "comprises a nitric acid containing liquid having a content of Pu'therein. The nitric acid solution also contains other materials, such as radioactive materials, of which the procedure of the present invention'aids in the elimination or reduction.

1 have found that certain supplemental flue-reagents, such as fluosilicic solid addition to a solution containing the Pu" and a'carrier in the above extraction and productprecipitationsfeps,causes the Pu to be carried away 'fromextraneous'matter more effectively. -I have further found that this action of-fiuosilicic acid and other comparable compoundsin givingbette'r sepaiatiombetter decontamination, and complexing orsolubilizing of radioactivity has numerous other applications inseparation and recovery 'processesof the class described.

Broadly, therefore, my invention may be applied to various solutions and particularly solutions containing high activities. The solutions to be processed by my invention'haveadded thereto such reagents as may be required, dependent upon the particular composition and condition of thesolution, to obtain the customary carrier precipitate formation at that particular phase of the process. Before, simultaneouslytherewith, or thereafter, as will befurther'apparent from the several examples, there is applied thereto the procedure of the present invention for causing "improved separation and particularly the elimination of gamma activity.

I'have found that by using fluosilicic acid or comparable compound,that processes for the recovery of Pu may be materially improved. I have found that fiuosilicic acid may be'employed in numerous different ways. In general, compounds of a formula H MF may be employed, examples of such other compounds being the acids of "titanium, boron and tin, more specifically exemplified by fluostannic 'o'r fiuotitanic acid. In the formula HgMF H represents hydrogen, ammonium, or other metallic or metalloid ions.

In further detail, examples "of 'some of the uses of fiuosilicic'acid areas follows: In the present extraction step, such as step ('2) above, it is usual to add a content of sulfate ion for complexing U as already briefly indicated above. However, this addition ofsulfate ion may be disadvantageous :in that it may precipitate a certain amount-of barium activity. It-has been found that the addition of fluosilicic acid in place of orin conjunction 'with sulfuric acid not 'only complexes the U, but lowers "7 the barium, zirconium and columbium activity precipitated. Also, the use of fluosilicic acid is less critical than in sulfuric acid and may be employed in uranyl nitrate solutions, as for example of a to 40% concentration and at temperatures as low as 35 C.

In the extraction step, fluosilicic acid or a like agent is added alone or in conjunction with a partial addition of sulfuric acid, the amount of either or both acids being sufiicient to complex in a soluble form at least one fourth of the U present in the solution. The acids may be added up to an amount such that the total acid is about 25% in excess of that required to complex the U, in which case the fluosilicic acid preferably should be about 50% to 100% of the total acid.

It is preferred, however, to use fluosilicic acid only and in an amount which will completely complex U.

I have also found that the addition of fluosilicic acid renders the active columbium and zirconium phosphates soluble and thereby prevents them from following the bismuth phosphate product precipitate in the above extraction step, thereby giving a higher decontamination. In addition to adding fluosilicic acid for rendering soluble the active zirconium and columbium materials, this procedure may be supplemented by adding inactive zirconium and columbium compounds. While the addition of fluosilicic acid substantially reduces the carrying by carrier precipitates of the zirconium and columbium activity, a small amount of this activity may still be carried by the bismuth phosphate precipitate. By adding, in addition to the fluosilicic acid, inactive potassium or ammonium fluozirconates which dilute the active fission products a still higher decontamination factor may be obtained.

Certain recovery processes for the waste liquors from the extraction step containing uranium and fission products may be carried out employing fluosilicic acid. It also appears that certain precipitates such as the sodium and potassium fluosilicates will carry fission products but not carry the uranium, thus permitting recovery of U free from fission products.

The present invention thus far is described in connection with extraction step (2) above. In addition, it may be employed, as will be apparent from the specific examples which follow, in the product precipitation step, for improving decontamination and for lessening product loss.

Referring next to the use of the present invention in the product precipitation step such as above described, in the product precipitation step, the solution treated comprises a nitric acid solution of Pu and fission activity which is the centrifugate resulting from the prior byproduct precipitation. To this oxidized solution, fluosilicic acid in amounts from 0.002 M up to an amount just insuflicient to cause precipitation of a metallic fiuosilicate, as for example sodium fluosilicate, may be added. The Pu solution may then be reduced and a regular BiPO product precipitate formed. Instead of fluosilicic acid, ammonium fluosilicate or other fluoreagents may be used, and the particular fluo-reagent chosen may be added either prior to, during, or after reduction and/or prior to, during or after the BiPO, product precipitation.

The addition of the fluo-reagent in the product precipitation step increases decontamination as a result of complexing zirconium and columbium fission activity in a soluble form.

The improvement in decontamination through the use of duo-reagents is so great that scavengers may be eliminated from the previous by-product precipitation step. The elimination of scavengers results in lower loss of Pu in the by-product precipitation step. Thus the use of duo-reagents results in higher product recovery in both the by-product precipitation and product precipitation steps with no sacrifice in overall decontamination. The above results are obtained regardless of whether or not scavengers are used in the by-product precipitation step.

If scavengers, such as zirconium, columbium, or tantalum are used in the by-product precipitation step, the scavenger fines passing through the centrifuge or filter are solubilized by the lino-reagents. If these fines, which contain relatively high amounts of fission products, are not solubilized prior to product precipitation, decontamination is reduced since the product precipitate which carries Pu also carries the fines. When the fines are solubilized with fluo-reagents prior to precipitation of the product, the associated fission activity tends to remain in solution and is not carried in the product precipitate. Thus decontamination is improved through the use of fiuo-reagents.

Other beneficial effects of the use of fluo-reagents include lower product losses in the product precipitation and greater ease of centrifugation or filtration of the product carrier due to increased crystal size of the carrier.

It has also been found that a method may be carried out by the addition of fluosilicic acid for complexing various activities, wherein decontamination may be accomplished by repeated precipitations without the alternate oxidation and reduction procedure now used.

There are a number of miscellaneous operations which may be carried out, as for example: The decontamination of equipment may be accomplished by washing the equipment with fluosilicic acid.

It is also possible to wash crystals of precipitates with fluosilicic acid solution for removing surface contamination without substantial Pu loss.

A still further understanding of my invention will be had by reference to the following detailed examples. In these examples the solutions containing Pu which were treated were, in general, the usual type encountered industrially, excepting that the gamma activity was in many instances perhaps higher than usual. That is, the solutions were obtained from standard processing and were approximately 1 normal in nitric acid, however, the invention is not limited to this normality. The solutions also may contain residual reducing agents, oxidizing or various inorganic acid and the like ingredients in addition to extraneous material, such as high activities.

Reference is now made to these specific examples:

Example I In accordance with this example, fluosilicic acid for sulfuric acid in for recovering Pu was carried out. As previously described uranyl nitrate solutions containing Pu, prior to the formation of a carrier precipitate therein, have heretofore been treated with sulfuric acid or other source of sulfate ion for complexing U. That is, the sulfate ion prevents the U from precipitating along with the Pu with the carrier precipitates formed for carrying down the Pu. However, while the sulfate ion satisfactorily complexes U, presumably it has been the cause of a certain amount of barium precipitating along with the Pu. Since the barium precipitating is strongly radioactive, the resultant Pu precipitate has been contaminated.

In accordance with the several runs carried out under this example, existing extraction procedure, as already described, was followed excepting that in place of the the substitution of the extraction cycle addition of sulfate ion usually made, fluosilicic acid was incorporated. It was found that fluosilicic acid complexed the U in a manner comparable to the sulfate ion, that it did not cause the substantial precipitation of active barium and in addition complexed zirconium and columbium as well, both of which are sources of gamma radiation. Therefore, the resultant extraction evidenced a higher decontamination factor in that the Pu material separated was freer of contamination. The results of runs under this example are summarized in the following table:

rouewtngame: 1

egseaaes TABLE 1 TABLE 2 .Gross. I, n new, 'Conc. "Gamma Acid in Percent Percent Percent Percent -Decon- Solution Description Mo'ls HzSlFu, Factor "Run No.= Extraction La Zr Cb Ba tatlinhia- Mols on Factor I H1. V. a Oxidized-Solution after Ge-Zr scaveng- I ing .03 4:5 11 1N HzSO4 10.0 72.9 11.2 2J6 "3J6 D0- .03 .05 11.19 12 1N HzSlFu. 16.2 69.2 10.5 .09 14.7 D0 .03 .025 10.0 13 1 N 112804-- 14 64.5 14 12 3.9 14 1 NH2SiFB--- 21.7 63.7 11.7 .05 16 As apparent from the table, an oxidlzed solution con- From the above table, which includes an analysis of the extraction precipitate, it can be seen that there is very much less Ba carried into the product (Pu) precipitate.

While in the preceding runs fluosilicic acid has been used to entirely replace the sulfuric acid addition, improved results may also be obtained by replacing only a part of the sulfuric acid by fluosilicic acid. It was also observed that while a uranyl nitrate solution having a concentration -of -20%, based on uranyl nitrate hexahydrate, sulphuric acid addition, the concentration bas'ed'on uranyl nitrate hexahydrate might vary from 10%40% with satisfactory results when using fluosilicic acid. Also it I was unnecessary to maintain the temperatures during the precipitation within particularly narrow ranges. When employing fluosilicic acid for complexing the extraction step may be carried out at temperatures varying from room temperatures to, for example, 85 C.

Example 11 ;In accordance with this example, the use of fluosilicic acid as an auxiliary to scavenging was carried out. A standard uranyl nitrate solution containing Pu was treated in the runs under this example. Standard bismuth phosphate product and by-product precipitates of the type already described were applied to the solution, leaving a nitric acid solution containing Pu To this solution the usual cerium and zirconium phosphate scavenger precipitate was formed, the function of which was to carry down at least a part of the residual activity which had not been carried down by the aforementioned by-product precipitate.

In the separation of'this cerium and zirconium scavenger precipitate industrially, centrifuges may not efiect a com- .plete removal of all of the finely divided residues. Consequently, when such scavenged solutions are thereafter reduced prior to making a product precipitate for carrying down Pu a certain amount of these fines may be carried down with the Pu" thereby contaminating the Pu .product with radioactivity.

In accordance with the present invention, it has been found that by adding a small-amount of fluosilicic acid to the solutions remaining after centrifugation that these taining 'Puwastreated with Pe as a reducing agent. Thereafter fiuosilicie was added in accordance with the present invention. By making counts in conventional manner onthe product precipitates the gamma decontamination factor 'inay be obtained. As may be seen, where fluosilicic 'acidliad been used the gamma factor was more than double that where no fluosilicic acid had beenused.

Example 111 In accordance with this example, several runs were carried outfor 'utiliiing fluosilicic acid as a substitute for scavengers. "In :the preceding 'example a scavenger step was included and after this scavenging the fluosilicic acid additions "were made. However, in accordance with the present example, the scavenging was omitted and the fluosilicic acid additions were made 'to the solution remaining after the by-product precipitate had been taken. In all other respects the process and materials were in accordance with existing procedure. That is, a uranyl nitrate solution containing Pu was processed which had been treated by existing bismuth phosphate product and by- .productpreeipitations to give a nitric acid solution Pu The Pu solution was then reduced with a ferrous reducing'agentand a regular bismuth phosphate product precipitate formed in the presence of fluosilicic acid. The results and details of the several runs in accordance with this example are sun'imariz cd below:

Run 1.-A straight BiPO by-product precipitate was applied in both cycles; the by-product precipitate was digested at 7 5 C for minutes. A straight BiPO; .product precipitation was applied in both cycles in presence of 0.05 M H SiF Run 2. -This run was the same as 1, except the byproduct precipitate was digested at room temperature for 30 minutes. i s I s Run 3.'I-n this run a PbSO addition with BiPO byproduct precipitate was made in both cycles (by-product digested at 30 minutes at C). A straight BiPO product precipitation was applied in both cycles in presence of 0.05 M H SiF Run 4. This run was the same 'as 3, except the byproduct precipitates were digested at room temperature for 30 minutes.

residual fines are complexed or solubilized in a manner that'the resultant Pu sepaai'ted will not be materially contaminat'ed thereby. In other words, the Pu p'roduct may be separateda's an improved product in that it evidences "a' higher "decontamination factor. The results of the In 'thepreceding'example the use of fluosilicic acid as a substitute for scz'ive'ng'ers'was described and the results indicated that the decontamination effected without the scavengers by means of fluosilicic acid alone was of a high "steer. r11 acearaaaee with the present example,

similar runs were carried out to further test the fiuosilicic acid substitution for scavengers, the present example distinguishing in that special study was madeof the quantity of plutonium recovered. In other words, it was desired to determine whether a high yield of plutonium could be recovered if fiuosilicic acid alone were used. The results of the runs in accordance with this example are sum- I marized below:

ous use of fiuosilicic acid or' salt was tested, namely the use of a solvent therefrom as a washing medium in certain steps in Pu separation and recovery processes where a water wash had been heretofore used.

in the existing operations product precipitates are frequently washed with water. In the centrifugation of such precipitates, a certain amount of fission activity is carried with the BiPO as sludgeof Zr, Cb and Si. It was l dF refers to the logarithm of the decontamination factor.

These runs showed, on the basis of plutonium losses, that fiuosilicic acid additions actually reduced the loss of plutonium compared with that experienced in the usual use of scavengers while at the same time giving satsifactory decontamination.

Example V In accordance with this example, a number of runs were carried out to determine the miscellaneous application of fiuosilicic acid addition to other phases of plutonium recovery. Under this example, plutonium containing precipitate was recrystallized both in the presence and absence of fiuosilicic acid. Details and results respecting these several runs are summarized below:

Run 1.-The Pu product precipitate was made in a solution of 10 N HNO diluted to l N. The solution was heated. to 75 C. and H PO added (over /fi hour) to make the solution 0.4 M therein; the precipitate was digested at 75 C. for one hour.

Run 2.-In this run Fe++ was added to the 10 N HNO solution of product precipitate so that final solution would be 0.03 M in Fe++ or Fe+++, or both, and then the solution was processed as in Run 1.

Run 3.--In this run Fe++ and H SiF were added to the 10 N I-INO solution of product precipitate to make a final solution 0.03 M in Fe++ or Fe+++, or both, and 0.05 M in H SiF The solution was then diluted to 1 N in I-INO and further processed as in Run 1.

Run 4.--In this run Fe++ and H SiF were added as in Run 3 and the resultant 10 N HNO solution of product precipitate containing this Fe++ and H SiF added drop by drop to a 0.4 M H PO solution at 75 C.

The results of these runs are summarized below:

From the results it may be observed that by the presence of fiuosilicic acid, not only was all of the plutonium recovered in the recrystallization as evidenced by the alpha count of the recrystallized product, but that the gamma contamination, when the fiuosilicic acid was present during the recrystallization of the product, was in some instances less than /5 of that initially present.

Example VI In accordance with this example another miscellanefound that this activity which was not held interstitially in the crystals was readily solubilized by fluoride containing compounds of the present invention. A few runs showed that solutions of (NHQ SiF and related compounds are particularly effective solvents. Such salts are advantageous in that they show surprisingly low corrosion rates at 40 C. in concentrations of five moles per liter. I

Three portions of an extraction precipitate containing Pu were washed with three equal portions of wash solution in the tests for which the data are shown in Table 6. The precipitate was in contact with each wash solution for thirty minutes before centrifuging.

TABLE 6 Percent Treatment Gamma Activity RBDJOVGQ There are numerous other instances where the use of fiuosilicic acid may be efiective. For exarnple, the equipment in which the various precipitations are carried out may become contaminated with strong activity accumulating on the equipment. It has been found that if such equipment is washed with solutions of fiuosilicic acid that this activity may be removed therefrom and the surfaces cleansed.

While it is not desired to be bound by any theory of operation, the following may illustrate to some extent the mechanism of the flue-type reagent of the present invention for decontaminating.

The efficacy of fiuosilicic acid and equivalent compounds as an aid to decontamination may be due to its acting as a reservoir of fluoride ions which form more stable complexes with zirconium, columbium and the various other elements than with silicon. Amounts of such complexed fluoride ion may be introduced into the system which would be prohibitive from the corrosion standpoint, if the fluoride ion were not so complexed. The following equation may be representative of the course of the reaction in, for example, complexing zircom'um.

In the above examples, the use of fiuosilicic acid has been principally described as this is the specific compound preferred from the industrial standpoint and is a readily available commercial material. However, the use of various derivatives such as ammonium and potassium salts thereof or the use of fluotitanic or other similar compounds may be employed in a co-rnp'a'r'able tniagner. For convenience of description all or these various fluorine containing reagents are designated as fluo-rejagents. As has been described, the fiuo=reagents may be used in a number of ways varying from'a'ssisting thes'precipitation steps to washing of. precipitates'and'even 'the'w'ashing of equipment in which'radioac tivematerials have been present. By the termcomplexing or 'solubilizing there is referred to the action described abovejof eliminating activity, presumably by rendering soluble elements or materials which cause this activity 'or constitute a source of the contamination. However, it ismot desired to'be bound by anytheory of operation,

-As indicated in the examples a relatively smallamoun't of fluo-reagentsuch as 05 M usually-suffices. H However, the invention is not limited in this respeCt and larger or smaller amounts, as for example,;from 0.002 lVI "to.l.00 M may be used. The upper limit of 1 .000 M depends on the solubility ofthe compounds fo'rmedby the-iluosilicate ions with the bismuth, iron, sodium "and-other ions present. So long as the lirnit ofzsolubility' is n'orexceeded, any amountup t mpon r may 'be used. within the broad limits of 0.002 -M to "1.000 :M, solubility controls and too much flue-reagent might precipitate the bismuth-fluosilicate, sodium fluosilicate, etc.

The decontamination accomplished may be determined in accordance with eonventionalprocedure and by .-me'ans of any of the usual instruments employed in-imeasuring radioactivity. That is, by using a Geigen-Mueller counter or equivalent device, the amount of gamma activity present in a sample may be measured before and aftertreatment and the amount of activity eliminated by the'treatment readily ascertained from this data. The term decontamination factor used herein is a comparative value or ratio derived by dividingtlie count valueor average of counts for series of runs -be'fore-anyv particular step-by that count value obtained after-thestep. overall decontamination factor is the valueob'tained by multiplying together several decontamination factors. The percentage of plutonium present or carried in a sample may be ascertained from the alphacount of the respective materials. In carrying out this invention, it is intended the best technique and equipment usually employed in handling and processing radioactive substances-will also be employed in the herein disclosed processes.

It is apparent from the foregoing description that fluo-reagents for the purpose of improving decontamination and product yield, maybe employed in connection with the BiPO process with or without scavengers. When used in the product precipitation step of the BiPO; process, in which no scavengers were employed in the byproduct precipitation ste it has many distinct advantages among which are: the processing time isreduced, the processing is simplified, waste disposal is renderedeasier, product yield is increased without an increase in. the volume handled, and losses in by-products are reduced.

In fact, the BiPO process, withoutseavengers and employing fluoreagents is the simplest knownprocessfor obtaining product in high yield and "free from contamination.

According to the best evidence'available, the oxidation state of plutonium secured in solution by the action of the oxidizing agents referred to herein and in cited cmpending application Ser. No. 519,714, now US. Patent N 2,785,- 951, is greater than four, and the oxidation state secured in solution by the action of the reducing agents referred to herein and therein is no greater than four. 7 It should therefore be understood that, asused herein, Pa and Pu in the (0) condition (or state) are 'both synonymous with plutonium in an oxidation state greater than four and Pu and Pu in the (r) condition (or s'tate) are both synonymous with plutonium in an oxidation state no greater than four."

It is to be understood that all matter-contained:inthe above description and examples shall be interpreted as "I4 illustrative and not limitative of the scope of this invention, and it is intended to claim the present inventiona's broadly as possible in view'of the prior art.

Having-thus described my invention, I claim:

1. In a carrier precipitation process for the separation and decontamination of plutonium values from contamination comprising uranium-fission-product values, including zirconium and columbium values, associated therewith in an aqueous solution comprising precipitating bismuth phosphate therein to carry plutonium therefrom, the improvement step for selectively removing uranium-fission- .product contamination concomitantly carried from the solution superficially upon the bismuth phosphate carrier precipitate, without removing a substantial amount of the plutonium content of the carrier precipitate, which comprises washing the formed bismuth phosphate carrier precipitate with an aqueous solution of a complex fluorinecontaining reagent having a structural formula:

H MF

where: His chosen from the group consisting of hydrogen, ammonium, and metallic and metalloid ions, M is a metal atom, F is a fluorine atom, and -x and y are whole numbers, to wash said contamination from the precipitate.

2. A process for the removal from a crystalline bismuth phosphate carrier precipitate of superficial contamination, including zirconium and columbium values, which comprises washing the precipitate with aqueous fluosilicic acid to wash said contamination from the precipitate.

3. In a'carrier precipitation process comprising the precipitation of bismuth phosphate in an aqueous nitric acid solution having dissolved therein uranium and uranium-fission-product values, followed by removal of the resulting bismuth phosphate precipitate from its supernatant liquid, the improvement method for mitigating co-precipitation of uranium and uranium-fission-product values during said precipitation of bismuth phosphate and for subsequently separating uranium-fission-product values from uranium values resultingly left remaining in said supernatant liquid after said removal of bismuth phosphate precipitate therefrom, which comprises adding and dissolving into said solution fluosilicic acid,'thereupon efiecting said bismuth phosphate precipitation in the presence of the added fluosilicic acid in the solution, and, after said removal of bismuth phosphate precipitate, precipitating, from said supernatant liquid, fluosilicate ion of the added fluosilicic acid resulting contained therein, as a fluosilicate salt chosen from the group there- 'of consisting of sodium fluosilicate and potassium fluotion of bismuth ions and phosphate ions in said solution to precipitate bismuth phosphate therein, and the subsequent separation and removal of the resulting carrier precipitate, the improvement step for enhancing the decontamination efiicacy of the process which comprises adding and dissolving into said solution, prior to said removal of carrier precipitate, a soluble complex fluorinecontaining reagent having a structural formula:

where: H is chosen from the group consisting of hydrogen, ammonium, and metallic and metalloid ions, is a metal atom, F is a fluorine atom, and x and y-are whole numbers, the concentration of said reagent in said solution being less than approximately 1 molar.

5. In a process for the separation and decontamination of plutonium values, by carrier precipitation thereof, from uranium and uranium-fission-product values associwhere: H is chosen from the group consisting of hydrogen, ammonium, and metallic and metalloid ions, M is a metal atom, F is a fluorine atom, and x and y are whole numbers, and efiecting said carrier precipitation in the presence of said reagent in solution.

6. In a carrier precipitation process for the separation and decontamination of plutonium values from contamination, including uranium and uranium-fission-product values, associated therewith in an aqueous solution, comprising precipitating bismuth phosphate therein to carry plutonium values therefrom, the improvement method for mitigating co-precipitation of uranium and uraniumfission-product values during said bismuth phosphate carrier precipitation, which comprises adding and dissolving into said solution, to a concentration less than approximately 1 molar, a soluble complex fluorine-containing reagent having a structural formula:

where: H is chosen from the group consisting of hydrogen, ammonium, and metallic and metalloid ions, M is a metal atom, F is a fluorine atom, and x and y are whole numbers, and providing a sufiicient concentration of bismuth ions and phosphate ions in the resulting solution to precipitate bismuth phosphate therein.

7. In a carrier precipitation process for the separation of plutonium values from uranium values associated therewith in an aqueous solution comprising precipitating bismuth phosphate therein to carry plutonium values therefrom, the improvement method for mitigating coprecipitation of uranium values during said bismuth phosphate carrier precipitation which comprises adding and dissolving into said solution fluosilicic acid to a concentration less than approximately 1 molar and providing of bismuth ions and phosphate bismuth a sufiicient concentration ions in the resulting solution to precipitate phosphate therein.

8. In a carrier precipitation process for the separation and decontamination of plutonium values from contamination comprising uranium-fission-product values, including zirconium and columbium values, associated therewith in an aqueous solution, comprising precipitating bismuth phosphate therein to carry plutonium values therefrom, the improvement method for mitigating coprecipitation of uranium-fission-product values during said bismuth phosphate carrier precipitation which comprises adding and dissolving into said solution fluosilicic acid to a concentration less than approximately 1 molar, and providing a suflicient concentration of bismuth ions and phosphate ions in the resulting solution to precipitate bismuth phosphate therein.

9. In a carrier precipitation process for the separation and decontamination of plutonium values from contamination, including uranium and zirconium, columbium, and barium uranium-fission-product values inherently associated therewith in an aqueous nitric acid solution of neutron-irradiated uranium, comprising providing a sufficient concentration of bismuth ions and phosphate ions in said solution to precipitate bismuth phosphate therein to carry plutonium values therefrom, the improvement method for mitigating co-precipitation of uranium values, and zirconium, columbium, and barium uraniumfission-product values during said bismuth phosphate carrier precipitation, which comprises adding and dissolving into said solution fluosilicic acid within the approximate range of 0.002 molar to 1 molar, while maintaining said solution at a uranium concentration equivalent to a uranyl nitrate hexahydrate proportion within the approximate range of 10% to 40% by weight thereof, at a temperature within the approximate range of 35 to C., at a nitric acid concentration of approximately normal, and in the presence of said fluosilicic acid therein. 10. In a carrier precipitation process comprising the precipitation, in an aqueous nitric acid solution, of a phosphate of a cation chosen from the group consisting of zirconium and columbium, followed by removal of a major portion of the resulting phosphate precipitate from its supernatant liquid, leaving a minor proportion thereof suspended in the supernatant liquid, and subsequently precipitating bismuth phosphate in said supernatant liquid, the improvement method for solubilizing said suspended phosphate precipitate in the supernatant prior to the hismuth phosphate precipitation and thereby mitigating the co-precipitation thereof during the bismuth phosphate precipitation, which comprises adding and dissolving into said supernatant to a concentration less than approximately 1 molar a soluble complex fluorine-containing reagent having a structural formula:

where: H is chosen from the group consisting of hydrogen, ammonium, and metallic and metalloid ions, M is a metal atom, F is a fluorine atom, and x and y are whole numbers, and providing a sufficient concentration of hismuth ions and phosphate ions in said supernatant to precipitate bismuth phosphate therein.

11. In the precipitation of bismuth phosphate as a carrier precipitate from an aqueous nitric acid solution, the method for increasing the crystal size of the formed bismuth phosphate precipitate which comprises adding and dissolving into said solution to a concentration less than approximately 1 molar a soluble complex fluorinecontaining reagent having a structural formula:

where: H is chosen from the group consisting of hydrogen, ammonium, and metallic and metalloid ions, M is a metal atom, F is a fluorine atom, and x and y are whole numbers, and providing a suflicient concentration of bismuth ions and phosphate ions in said solution to precipitate bismuth phosphate therein.

12. In a carrier precipitation process for the separation and decontamination of plutonium values from contamination, including uranium and uranium-fission-pro'duct values, associated therewith in an aqueous solution, comprising precipitating bismuth phosphate therein to carry plutonium values therefrom, the improvement method for mitigating co-precipitation of uranium and uranium-fission-product values'during said bismuth phosphate carrier precipitation, which comprises adding and dissolving into said solution a soluble complex fluorine-containing reagent chosen from the group consisting of fiuosilicic, fluostannic, and fiuotitanic acids to a concentration less than approximately 1 molar, and providing a sufiicient concentration of bismuth ions and phosphate ions in said solution to precipitate bismuth phosphate therein.

13. In a process comprising precipitating bismuth phosphate in an aqueous solution contaminated with uraniumfission-product values, the improvement method for removing uranium-fission-product contamination concomitantly carried from solution by the bismuth phosphate precipitate, which comprises dissolving said bismuth phosphate precipitate in acid, recrystallizing bismuth phosphate by reducing the acidity of the resulting solution, adding phosphoric acid and a soluble complex fluorinecontaining reagent having a structural formula:

H MF, where! H is chosen from the group consisting of hydrogen, ammonium, and metallic and metalloid ions, M is a metal atom, F is a fluorine atom, and x and y are whole numbers, said reagent being present in a concentration less than approximately 1 molar, thereby leaving uraniumfission-product contamination in the complex-reagent containing supernatant solution.

14. In a carrier precipitation process for the separation and decontamination of plutonium values from contamination comprising uranium-fission-product values associated therewith in an aqueous solution, comprising precipitating bismuth phosphate therein to carry plutonium values therefrom, the improvement method for removing uranium-fission-product contamination concomitantly carried from solution by the bismuth phosphate carrier precipitate which comprises dissolving said bismuth phosphate precipitate in acid, recrystallizing bismuth phosphate by reducing the acidity of the resulting solution, adding phosphoric acid and a soluble complex fluorinecontaining reagent having structural formula:

H MF

where: H is chosen from the group consisting of hydrogen, ammonium, and metallic and metalloid ions, M is a metal atom, F is a fluorine atom, and x and y are whole numbers, said reagent being present in a concentration less than approximately 1 molar, thereby recarrying plutonium values with the recrystallized carrier precipitate while leaving uranium-fission-product contamination in the comp!ex-reagent-containing supernatant solution.

15. The process of claim 14 wherein said soluble complex-fluorine-containing reagent is fluosilicic acid.

16. In a carrier precipitation process for the separation and decontamination of plutonium values from contamination comprising uranium fission-product values, including zirconium and columbium values, associated therewith in an aqueous solution, comprising precipitating bis,- muth phosphate therein to carry plutonium values therefrom, the improvement method for removing uraniumfission-product contamination concomitantly carried from solution by the bismuth phosphate carrier precipitate which comprises dissolution of said bismuth phosphate carrier precipitate in substantially 10 normal nitric acid followed by recrystallization thereof by means of: incorporation of fluosilicic acid into the resulting solution to a concentration no greater than approximately 1 molar, dilution thereof to substantially one normal in nitric acid, and incorporation of phosphoric acid therein; thereby recarrying plutonium values with the recrystallized carrier precipitate while leaving uranium-fission-product contamination in the fluosilicic-acid-containing supernatant solution.

References Cited in the file of this patent McMillan et al.: Radioactive Element 93, Physical Review, vol. 57, pages 11856, 1940. (Copy in Scientific Library.)

Hahn et al.: Chemical Abstracts, vol. 36, page 6893 (1942).

UNITED STATES PATENT OFFICE Certificate of Correction Patent No. 2,886,408 May 12, 1959 Glenn W. Stahl It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 36, strike out solid; column 9, line 22, before sulphuric insert Was customarily used with the; line 70, for sepaarted read separated; column 10, line 33, after solution insert -containing; column 12, lines 66 to 69, the formula should appear as shown below instead of as in the patent:

SiF 2H O SiO 4H' 6F- ZrFf column 15, line 4, after method insert for.

Signed and sealed this 10th day of November 1959.

Attest:

KARL H. AXLINE, ROBERT C. WATSON, Attestz'ng Oficer. Gonwm'esz'oner of Patents.

UNITED STATES PATENT OFFICE Certificate of Correction Patent No. 2,886,408 May 12, 1959 Glenn W. Stahl It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 36, strike out solid; column 9, line 22, before sulphuric insert was customarily used with the-; line 70, for sepaarted read separated; column 10, line 33, after solution insert containing; column 12, lines 66 to 69, the formula should appear as shown below instead of as in the patent:

lTZr ZrFf' column 15, line 4, after method'insert -for--.

Signed and sealed this 10th day of November 1959.

Attest:

KARL H. AXLINE, ROBERT C. WATSON,

Attestz'ng Oficer. Oomnissz'oner of Patents. 

1. IN A CARRIER PRECIPITATION PROCESS FOR THE SEPARATION AND DECONTAIMINATION OF PLUTONIUM VALUES FROM CONTAINNATION COMPRISING URANIUM-FISSION-PRODUCT VALUES, INCLUDING ZIRCONIUM AND COLUMBIUM VALUES, ASSOCIATED THEREWITHIN AN AQUEOUS SOLUTION COMPRISING PRECIPITATING BISMUTH PHOSPHATE THEREIN TO CARRY PLUTONIUM THEREFROM, THE MPROVEMENT STEP FOR SELECTIVELY REMOVING URANIUM-FISSIONPRODUCT CONTAMINATION CONCOMITANTLY CARRIED FROM THE SOLUTION SUPERFICIALLY UPON THE BISMUTH PHOSPHATE CARRIER PRECIPITATE, WITHOUT REMOVING A SUBSTANTIAL AMOUNT OF THE PLUATONIUM CONTENT OF THE CARRIER PRECIPIATE, WHICH COMPRISES WASHING THE FORMED BISMUTH PHOSPHATE CARRIER PRECIPITATE WITH AN AQUEOUS SOLUTION OF A COMPLEX FLUORINECONTAINING REAGENT HAVING A STRUCTURAL FORMULA: 